1. Field of the Present Invention
The present invention relates to a lithium secondary battery and method for manufacturing the same.
2. Description of the Related Art
In recent years, as one of innovative secondary batteries with a high power and a high energy density, a lithium secondary battery using a nonaqueous electrolyte and chargeable by moving lithium ion between a positive electrode and a negative electrode has been utilized.
Due to its high energy density, lithium secondary batteries have been used practically and become popular as power sources for electronic portable appliances of information technology such as note-type personal computers and mobile phones. In future, owing to further compactness and higher functionality required for these portable appliances, it is expected to increase the load on the lithium secondary batteries as power sources. Therefore, the requirement of high energy density for the lithium secondary batteries has been increased very high.
To increase the energy density of a battery, use of a material having higher energy density as an active material is effective means. Accordingly, recently, in the lithium secondary batteries, alloy materials of elements such as Al, Sn, and Si storing lithium by alloying with lithium have been proposed and investigated as negative-electrode active material having high energy density in place of graphite which is presently used practically.
However, in the electrodes for which such materials alloying with lithium are used as active material, since the volume of the active material is expanded/shrunk at the time of storage (intercalate) /release (deintercalate) of lithium, there occurs a problem that the active material is pulverized and separated from current collectors to result in current collection deterioration in the electrodes and charge-discharge cycle property deterioration.
The applicant of the present invention has found that with respect to an electrode using a silicon-containing material as a negative-electrode active material to be alloyed with lithium, a negative electrode formed by sintering a mixture layer containing active material of the silicon-containing material and a binder on the surface of a current collector of a surface-roughened conductive metal foil in a non-oxidizing atmosphere exhibits high current collection capability in the electrode owing to the high adhesion property of the mixture layer and the current collector and thus provides good charge-discharge cycle property (Japanese Patent Application Laid-Open No. 2002-260637).
However, in the case of using the above-mentioned negative electrode, investigations in details on what battery structure is excellent in the charge-discharge cycle property have not been made yet.